In a typical die bonding process, semiconductor dice are detached and lifted from a film frame comprising plastic adhesive film or a Mylar film and are then transferred to a substrate such as a lead frame or printed wiring board (PWB) substrate. Typically, in a pick-up process, a designated die will first be aligned and moved to a location where push-up pins will rise to raise the die from below while the plastic adhesive film is held down by vacuum suction. The die will be detached from the plastic adhesive film when the push-up pins rise to an appropriate level. A collet or pick-up tool which is positioned just above the top surface of the die provides vacuum suction to pick up the detached die from the plastic adhesive film and transfers the die to a bonding substrate.
Conventionally, for small dice (for example, having less than 2 mm in width), one ejector pin positioned at the center of the die to be detached is used. However, for larger dice, multiple ejector pins are used in order to evenly distribute the push-up force on the die and reduce a pinching effect by the ejector pins. A prior art example of a die detachment apparatus disclosing the use of multiple round top push-up pins is U.S. Pat. No. 6,201,306 entitled “Push-up Pin of a Semiconductor Element Pushing-up Device, and a Method for Separating”. Localized stress is generated by the push-up force of the pins and one way to reduce this stress is by using pins with different geometries such as round tops. Multiple round top push-up pins are operative to project upwards through a vacuum platform to detach a die from an adhesive tape.
When the dice get thinner, especially in the case of stacked dice in an electronic package, there is always a chance that a die may break or crack during the detachment process of the die from the plastic adhesive film. The breakage of the die is primarily due to the fact that the stress induced by the pushing up of the pins reaches the critical failure bending stress of the die before the delamination of the interface between the die and the plastic adhesive film takes place. This will be more problematic for (i) dice of bigger size, (ii) thinner dice, and (iii) attachments where there is a stronger adhesion force between the die and the plastic adhesive film.
Special techniques for detaching thin dice are exhibited in the prior art, such as employing projecting tools having lateral movement. U.S. Pat. No. 7,240,422 entitled “Apparatus and Method for Semiconductor Chip Detachment” shows an example of a prior art die detachment tool which discloses the use of laterally moving projecting tools for detaching thin dice. It includes a die detachment tool with projecting tools having curved top surfaces. The projecting tools are of pre-determined width and project upwards from a vacuum platform to push and lift the die so as to detach it from an adhesive tape while the adhesive tape is pulled away from the die by vacuum suction provided at the platform. Using this technique, it is necessary for the projecting tools to move slower than the propagation speed of the delamination process so that delamination is complete. Therefore, the cycle time is longer as compared to using vertical push-up pins to detach dice.
Another prior art die detachment tool is disclosed in US Patent Publication No. US2006/0252233 entitled “Semiconductor Device and its Manufacturing Methods”. The die detachment tool therein applies ultrasonic vibration to an upthrow pin for detaching thin dice from an adhesive tape. The heat and micro-vibration induced by the ultrasonic vibration enhance the delamination between the die and the adhesive tape. The drawback to this method relates to the use of an ultrasonic vibrator such as a transducer horn, which requires optimization in relation to the geometry of an upthrow pin and the type of adhesive tape used. Developing a customized application tool is necessary for different dice and adhesive tape combinations and this consumes a lot of time. In addition, the heat generated by the ultrasonic vibration needs to be controlled to prevent excessive deformation of the adhesive tape.
Therefore, it would be desirable to provide an apparatus and method for detaching thin dice from an adhesive tape while avoiding die cracking or deformation of the adhesive tape, and shortening cycle time.